582 The American Naturalist. [July, 
ference, and lead only to the death of cells. These abnormal- 
ities are the ones described in the sequel, while other classes 
of abnormalities are either obtained by other methods applied 
to the egg of the same animal or else refer to the egg of the 
sea urchin, Strongylocentrotus lividus, and are not mentioned in 
detail in the present paper. 
Wounding the cells of Ascidia aspera in early stages leads to 
the death of these cells and to subsequent abnormalities of 
development identical with those resulting when the cells die 
naturally or without apparent cause. 
The method of inflicting injuries upon one or more cells of 
the minute eggs studied by M. Chabry is as simple in princi- -_ 
ple as it is successful in operation, given sufficient delicacy in 
manipulation. The eggs are observed under the microscope 
in capillary tubes of glass, each egg lying without undue 
pressure in a separate tube of right diameter. The tube is 
mounted in water and covered by a cover glass so that a clear 
view of the egg is obtained with quite high powers. To see 
all sides of the egg the tube is revolved by a small crank and 
wheel attached to one end, turning freely in two rings of glass 
fixed to the microscopic slide. 
The other end of the tube bears the exceedingly sharp 
pointed needle that is to perforate the egg. This needle is the 
most difficult part of the apparatus to manufacture, being 4 
glass rod drawn out to a point of excessive acuteness and also 
straight. When once made the needles are provided with a 
protecting piece of capillary tubule, which may either pass 
into the capillary containing the egg or else be joined to its 
end by a surrounding tube according as the egg capillary is 
large or very small. To move the glass dart in and out, 
towards and away from the egg when it has been first rightly 
adjusted, a small lever attached to the microscope by an inge- _ 
nious and simple arrangement of spring and screw enables 
one to thrust the point, whilé observing it under the micro- 
scope, into the egg for a given distance and not further, and 
then to withdraw it quickly. Thus stabs are made that need 
affect but a single cell and any known and chosen cell. : 
